Protective system



Oct. 23, 1951 H wlTTENBERG 2,572,292

PROTECTIVE SYSTEM Filed May 3, 1946 EL, EL? A47- T0 GREEN SIG/VALS INVENTOR. Huberl'l. W17 elzberg BY @M Patented Oct. 23, 1951 PROTECTIVE SYSTEM Hubert H. Wittenberg, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application May 3, 1946, Serial No. 666,977

2 Claims. l

This invention relates to protective systems such as are designed to produce an eiiect in response to values of impedance which are outside the range of resistances or impedances normally existing between one end of the rails of a section of railroad or the like. One protective system of this character is disclosed by my copending application Serial No. 631,723 filed November 29, 1945, now Patent No. 2,460,160. The present invention is an improvement on the invention of the aforesaid application in that it operates with greater precision to provide a danger signal when the impedance between one end of the rails or conductors decreases below its normal range of values or when such resistance or impedance exceeds its normal range.

It is well known that the impedance between the rails of a railway section or crossover varies from a relatively high value approaching iniinity in dry weather to a relatively low value in wet weather. This variation in impedance is herein designated as the normal range of the impedance or resistance between the rails. When such impedance assumes an abnormal value, it is desirable that this condition be indicated immediately by a danger signal such as a red light.

It is obvious however that if a break occurs in the rails a device placed at one end would not be able to detect an abnormal impedance beyond the break. In order to care for this contingency a rectifier is placed at the far end of the block in question, just as in my application Serial No. 631,723. To voltage of such a polarity as to make a current flow in a forward direction through the rectiiier the impedance appears as a very low value. This is also a normal value. Hence there is an abnormal range of impedances having an upper and lower limit which is monitored by the invention about to :be described.

In accordance with one modification of the present invention, this result is achieved by a protective system including a bridge circuit which (1) has as the unknown arm the rails of the railway section which are interconnected at their far end through a unilateral impedance such as a rectifier, (2) has applied to its input terminals an alternating potential of peaked wave form, and (3) has an indicator connected to its output terminals consisting of a vacuum tube circuit which includes a single tube stage followed by a stage including a pair of thyratrons connected in push-pull relationship.

As is well known in the art, impedances in the unknown arm of a bridge above the balance value produce a negative output voltage say, when the input voltage is positive and conversely,

unknown impedances below the balance value produce a negative output voltage when the input voltage is negative. My invention utilizes the rst of these unbalanced conditions to check for normal impedances or a clear track, and the second to check for below abnormal or continuity of the rails through an articial short in the form of the rectifier. The indicator is sensitive only to negative signals and if either negative signal disappears the indicator is deenergized and a danger signal appears. The use of an alternating current of peaked wave form has the advantage that the positive and negative testing peaks are spaced from one another so that more sensitive operation of the apparatus is realized and the average rectified current is restricted to a value sufficiently low to prevent overheating of the rectifier.

Important objects of the present invention are to provide an improved protective system and method of operation which make available a greater degree of precision than that heretofore realized in connection with systems designed to produce a signal in response to impedance values outside a predetermined normal range.

The invention will be better understood from theV following description considered in connection with the accompanying drawings and its scope is indicated yby the appended claims.

The single iigure illustrates the form of the invention which is outlined above,

This form of the invention includes a source I0 of alternating potential having a peaked wave form, a bridge I I, a single stage I2 and an output push-pull stage I3.

The bridge circuit includes three resistors R1, R2 and R3 and a pair of rails or conductors I4 and I5 which are interconnected at their far ends through a rectifier I6 and have between them an impedance R4 which varies over a predetermined normal range. The alternating potential of peaked wave form is applied to the bridge II through one pair of leads Il and I8 and potential resulting from change in the unbalance of the bridge is applied through leads I9 and 20 to the input circuit of the single stage I2.

The alternating potential of peaked wave form is derived from a sixty cycle input transformer 2I which has one terminal of its secondary winding 22 connected through a resistor 23 to the anode 24 and cathode 29 of the electron discharge devices V4 and V2 and has the other terminal of this secondary winding 22 connected through an inductor 25 to the lead I1 of the bridge II. The secondary winding 22 and resistor 23 are shunted Iby a capacitor 2'I. The

cathode 28 and anode 25 of the devices V1 and V2 are connected to the lead i8. The input circuits for V1 and V2 and well known phase shifting circuits connected as ollows: The inidpoint terminals of the secondary windings 39 and 3| of a pair of transformers 462 and 33 are connected respectively to the cathodes 28 and 29 of devices V1 and V2. From the secondary winding 36, alternating potential is applied through a capacitor 54 and resistors 55 and 35 to the grid 31 of the gaseous discharge device V1. Similarly from the winding i', alternating potential is applied through Va capacitor 56 and resistors 39 and 49 to the grid 4l of the gaseous discharge device V2.

The phase relation between the alternating potentials applied to the grids 31 and 4i, and the corresponding anodes 24 and 25 is such that the device V1 conducts current only during a predetermined part of the positive half cycie oi the sixty cycle input and the device V2 conducts current only during a predetermined part of the negative half cycle of the sixty cycle input. fis V1 begins conduction capacitor 21 discharges through the series combination of V1, inductanoe 26, and the bridge. A large pulse of current ilows through this series circuit since the bridge resistance is small. Following this pulse there is a small current, as determined by the relative large resistor 23, that flows until the A.-C. potential from secondary 22 passes through zero. Device V2 and its associated' circuit operate in a similar manner to produce a negative pulse 189 later.

The single stage l2 includes an electron discharge device V3 having an input circuit which includes the bridge l l, a grid resistor 42 and a cathode bias resistor 43 which is shunted by an alternating current bypass capacitor 44. The output circuit of the device V3 includes an anode resistor 45 and the resistor 43.

From the anode terminal of the resistor 45, a potential dependent on the current of the device Va is applied through a coupling capacitor 46, resistors 4'! and 46, and resistors 46 and 59 to the grids 5I and 52 of the push-pull connected gaseous discharge devices V4 and V5. It will be noted (1) that the resistors 47 and 48 are partly shunted by bypass capacitors 53 and 54, (2) that alternating bias potential is applied to the shield grids 55 and 55 i the devices V5 and V4 from a secondary winding 57, (3) that the output circuit of the device V5 includes a relay winding R112, a secondary winding 58, the shield grid 55 and the lower half of the winding 5i, and (4) that the output circuit of the device V4 includes a relay winding R111, a secondary 59, the shield grid 56 and the upper half of the winding 5i. The polarities of the windings t?, 55 and 59 are such that the shield grid and anode potentials of the devices V4 and V5 are opposed. The relays RL1 and R112 are related in a well known manner so that deenergization of either of them produces a signal indicating the existence of an abnormal impedance between the monitored ends of the conductors I4 and i5.

Under these conditions, both relays are energized so long as the monitored impedance R4 remains within its normal range. When the impedance R4 becomes lower than the lower limit of its normal range and the terminal I6 is negative. the bridf'e more nearly balances and o less negative potential is applied to the control grid 59 of the device V3 which takes more current and applies to the grids 5l and 52 a more negative potential whereby the device V4 and the relay R111 are deenergized. When a crack or break occurs in the rails, the rectiiier I6 is not able to present its normal low impedance to the positive pulse on terminal I8: at the next positive peak (terminal I8 positive) the bridge balances or unbalances in the other direction giving a more positive signal to V3. As a result V5 and its relay R112 are deenergized.

The .outstanding characteristic of the present invention is the provision of a bridge network which functions in response to an alternating potential of peaked wave form with a high degree of precision to produce a signal when the impedance between two conductors varies outside its normal range.

I claim as my invention:

1. The combination of a pair of conductors interconnected through `a leakage impedance having -a normal range of variation, a bridge circuit having a pair of input and a pair or" output terminals respectively across different diagonale of the bridge and having kone ci its arms connected to said conductors at one or their ends, means for applying an alternating potential to said input terminals, means connected between said conductors at the other of their ends for presenting a relatively low impedance to potential of one polarity and a relatively high inpedance to potential of the opposite polarity, means for deriving from said output terminals a control potential which increases in one polarity sense in one condition of input polarityV when said leakage impedance decreases belet.7 the lower limit of its normal range of variation, and which increases in the same said polarity sense in another condition of input polarity when said impedance exceeds the upper limit ci its normal range, due to the bridge reversing polarity characteristic for these diiierent conditions, and means responsive to said control potentials when and only when said control potential increases in said one polarity sense beyond predetermined values.

2. The combination claimed in claim 1said alternating potential being oi peaked wave form.

HUBERT H. WITTENBFEt-G.

REFERENCES CITED The following references are of record in the nl@ oi this patent:

UNITED STATES PATENTS Number Name Date 1,765,715 Byers June 24, V1939 1,824,128 Duffy et al Sept. 22, 1931 1,951,461 Wilson Mar. 26, 1934 1,969,059 Bodde Aug. 7, 1934 2,083,920 Powell June l5, 1937 2,095,684 Witmer et al, Oct. 12, 1937 2,098,041 Hoppe Nov. 2, 1937 2,123,966 Rees July 19, 1938 2,182,163 Place Dec. 5, 1939 2,290,446 Pflasterer July 21, 1942 2,366,500 Eastin Jan. 2, 1945 2,418,869 Copley Apr. 15, 194'? 2,420,578 Wilson May 13, 1947 2,466,746 Shive Apr. 12, 1949 2,467,856 Rich Apr. 19, 1949 2,484,342 Hart Oct. 1l, 1949 OTHER REFERENCES Taylor, abstract of application 627,733, published Sept. 5, 1950, O` G. vol. 638. 

